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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 21 |
| 3 | 24 |
| 4 | 60 |
| 5 | 210 |
| 6 | 637 |
| 7 | 1840 |
| 8 | 5792 |
| 9 | 18556 |
| 10 | 54034 |
| 11 | 160246 |
| 12 | 499140 |
| 13 | 1501706 |
| 14 | 4627363 |
| 15 | 13954490 |
| 16 | 43064736 |
| 17 | 131174878 |
| 18 | 399170874 |
| 19 | 1222825766 |
| 20 | 3739040310 |
| 21 | 11456400210 |
| 22 | 35068696769 |
| 23 | 107362206600 |
| 24 | 329271410590 |
| 25 | 1009129910706 |
| 26 | 3096269613087 |
[4,21,24,60,210,637,1840,5792,18556,54034,160246, 499140,1501706,4627363,13954490,43064736, 131174878,399170874,1222825766,3739040310, 11456400210,35068696769,107362206600,329271410590, 1009129910706,3096269613087] |